With development of mobile communications technologies and increasingly high requirements of mobile communications users, application scenarios of the mobile communications technologies are becoming more complex. For a mobile communications system, various signal systems may coexist for a long period of time, so as to adapt to a more complex mobile communications application scenario. A power amplifier PA is an important composition part of a radio frequency processing unit RRU (Radio Remote Unit) of a mobile communications system. Nonlinearity and a memory effect of the PA may cause nonlinear distortion of a signal output by the power amplifier, resulting in distortion of the signal output by the PA and an increase in leakage of out-of-band power of the signal, and in a severe case, a receiver cannot correctly receive the signal and interference is caused to a communications system in an adjacent frequency band. Usually, a digital pre-distortion technology DPD and an RRU that has multiple frequency bands, multiple systems, and an ultra-wideband characteristic are used to reduce nonlinear distortion of the signal output by the PA. Generally, a DPD module is designed before the PA. A nonlinear distortion generated by a digital intermediate frequency signal by using the DPD module and a nonlinear distortion generated by the PA cancel out each other, thereby improving a degree of linearity of an output of the PA.
In the prior art, a feedback signal and a signal that is output by a predistortion circuit are used as input signals of a predistortion coefficient learning circuit. Predistortion model coefficient training is separately performed on each frequency band, to obtain nonlinear model coefficients corresponding to N frequency bands. A predistortion coefficient obtained after the training is replicated for a predistortion circuit. Nonlinear modeling of the predistortion circuit is then performed for a power amplifier according to the predistortion coefficient.
However, in a wideband communications system, a design of an ultra wideband power amplifier is limited by device performance, and it is difficult to optimize low frequency envelop impedance. An insufficient video bandwidth causes a relatively strong electrical memory effect of a power amplifier. In addition, a harmonic frequency range is wider, it is also difficult to optimize harmonic impedance, and enhancement of the electrical memory effect is also caused. In a conventional digital predistortion technology, a feedback channel feeds back only a fundamental wave signal, and cannot feed back a fundamental wave signal and a harmonic signal in real time. As a result, a predistortion processing circuit can perform nonlinear modeling of a predistortion circuit by using only information about the fundamental wave signal, and cannot perform nonlinear modeling of the predistortion circuit in real time by using information included in an envelope signal and a harmonic signal that are output by a power amplifier, causing lowered accuracy of nonlinear modeling of the predistortion circuit and a degraded performance indicator of the predistortion circuit.